As is known in the art, achieving both high efficiency and high linearity in radio frequency (RF) power amplifier systems is a longstanding challenge. One means of improving efficiency in such systems is an architecture wherein the power amplifier system is switched with discrete transitions among a set of operating states. For example, this includes an RF amplifier system in which the drain bias voltage for the one or more power amplifiers provided as part of the RF power amplifier system is dynamically selected from more than one possible source or level (e.g., selected from among multiple discrete supply voltages.)
A range of power amplifier systems exist in which the drain bias for one or more power amplifiers forming the power amplifier system is provided via dynamic selection from among a plurality of sources. For example, some systems dynamically select drain bias voltages from among a discrete set of input supply voltages and then provide additional regulation to provide a continuously-varying drain voltage (e.g., for partially realizing a desired envelope in the output). Other prior art systems directly exploit discrete drain levels, including “class G” amplifiers, multi-level LINC (MLINC) Power Amplifiers, Asymmetric Multilevel Outphasing (AMO) Power Amplifiers, and Multilevel Rackoff amplifiers.